Problem: Solve for $x$ and $y$ using substitution. ${4x+4y = 4}$ ${x = y+7}$
Explanation: Since $x$ has already been solved for, substitute $y+7$ for $x$ in the first equation. ${4}{(y+7)}{+ 4y = 4}$ Simplify and solve for $y$ $4y+28 + 4y = 4$ $8y+28 = 4$ $8y+28{-28} = 4{-28}$ $8y = -24$ $\dfrac{8y}{{8}} = \dfrac{-24}{{8}}$ ${y = -3}$ Now that you know ${y = -3}$ , plug it back into $\thinspace {x = y+7}\thinspace$ to find $x$ ${x = }{(-3)}{ + 7}$ ${x = 4}$ You can also plug ${y = -3}$ into $\thinspace {4x+4y = 4}\thinspace$ and get the same answer for $x$ : ${4x + 4}{(-3)}{= 4}$ ${x = 4}$